Photographic color correction process



June 17, 1952 c, GRESHAM 2,600,756

'PHOTOGRAPHIC COLOR CORRECTIONP ROCESS Fired Oct. 15, 1948 IO II F W7! V //JJ BLUE RECORD NEGATIVE l2 /3 F/GJ. w r L/fi A41 YI'AJ GREEN- RECORD n/Eanr/vE l5 l4 l5 r V/ ///Z 1/11! I ISL/1A RED REORD NEGflTIl/E aw: fiECaRD Pos/r/vE PR/mmY RELIEF DYED YELLOW- GREEN RECORD Pas/11v: Pn/Mmr RELIEF DYED MflGENTfl GREEN RECORD POSITIVE SECONDHRY RELIEF UNDYED 4 F/ RE D RECORD P 5! TI l/E SECONDHRY RELIEF UNDYED BLUE fiicoRo' PRIMRRY RELIEF squzzae'zo WITH GREEN RECORD sEco/vpnm' RELIEF GREEN RECORD Pn/Mnny RELIEF svusssam WITH RED RECORD secarwnm' RELIEF $51 or comun- SEPIIRIITION RELIEFS calms-c150 F02 BLUE ABSORPTION BY MHGENTH DYE AND GREEN HBSQRPTION 5v CYflN 0Y5 DONALD C. GRESHAM Inventor y 4 W, (fa

Patented June 17, 1952 PHOTOGRAPHIC COLOR CORRECTION PROCESS Donald C. Gresham, Wealdstone, England, as-

signor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application October 13, 1948, Serial No. 54,328 In Great Britain October 17, 1947 6 Claims.

This invention relates to colour photographic processes and particularly to a method of producing colour-correction of coloured photographic images produced by dye-imbibition.

It is well known that the dyes or colouring material used to form coloured images in threecolour photographic processes undesirably absorb light in the region of the spectrum where the highest transmission is desired, as is more fully discussed in Evans U. S. Patent 2,203,653, Evans and Hanson U. S. Patent 2,371,746 and elsewhere.

In dye-imbibition processes of colour photography there is produced a number, usually three, of colour separation records in the form of relief images which aredyed to the requisite colours and these are used to produce superimposed dye-images giving a subtractively coloured multi-colour image. Usually, the three colour-separation relief images are respectively a positive record of the blue which is dyed yellow, a positive record of the green which is dyed magenta and a positive record of the red which is dyed cyan. These may be bound in superimposition or the dye-images transferred to a single support in superimposition.

For convenience in the present specification, the reliefs which are used directly in this way for forming the superimposed images will be referred to as primary reliefs, since the invention employs further reliefs which are not so used directly and these will be referred to as secondary reliefs.

One object of my invention is to provide a method of modifying the amount of dye absorbed in one or more of a set of dyed colour separation relief images to give colour correction for unwanted absorption. Another object is to provide a method of modifying the amounts of dye absorbed in one or more of a set of dyed colour separation relief images to give tone correction. A further object is to provide a method of modifying the amounts of dye absorbed in one or more of a set of dyed colour separation relief images to give both colour and tone correction. Other objects of my invention will be come apparent from the following description.

In one form of my invention, correction for unwanted absorption of a colour by dye in one of a set of dyed colour separation relief images is obtained by removing dye from the dyed (primary) relief image which records the colour which is unwantedly absorbed by bringing it into contact and in register with an undyed (secondary) relief image which is a replica of the said dyed relief image bearing the said unwanted absorption. For example,'undesired absorption of blue light by a magenta dye (in a green record colour separation relief image) may be corrected by pressing the blue record primary relief (dyed yellow) into contact with an undyed green record secondary relief. It is apparent that the undyed green record secondary relief should be laterally reversed comparedwith the dyed primary relief image. This method may be used for the correction of unwanted absorption of one ormore colours by one or more dyes in the same set of relief images by performing contacting operations between the appropriate dyed primary and undyed secondary reliefs according to the invention.

In a modification of this process, where the three dyed relief images are to be bound together to form the desired three colour picture (normally a transparency), the cyan relief and the magenta relief can be made laterally reversed compared with the yellow relief, in which case it is not essential to make special secondary reliefs since the cyan and magenta reliefs can be used v(prior to being dyed) as temporary secondary reliefs for pressing into contact with the yellow relief in order to bleed dye therefrom to obtain colour correction for the undesired blue absorptions of the cyan and magenta dyes. Alternatively, if only one of these is laterally reversed, for instance the cyan relief, this can be used to bleed dye from both the yellow" and the magenta reliefs to obtain colour correction for the undesired blue and green absorption of the cyan dye. Of course, in all cases where a relief is so used for bleeding dye from another relief it must be suitably washed thereafter to remove all or most of such dye before it is used as the final dyed relief.

In another form of the invention, tone modification of a photographic relief image for compensating for errors elsewhere in a process such as a photolitho process is obtained by pressing the undyed relief ,image into contact with a uniform dyed gelatine layer. Alternatively, the relief image may be dyed at more than the normal concentrationand pressed into contact with a uniform undyed gelatine layer.

As far as we are aware it has not before been realized that it is possible to advantageously'influence the amounts of dye taken up by a relief image to produce tone correction, by causing the dye to be shared between the relief image and the plain colloid layer.

In another form of the invention, colour correction combined with tone correction may be obtained by forming the secondary relief referred to above by giving less exposure to it than when no tone correction is desired, and preferably also making the contrast greater than when no tone correction is desired, and then using this secondary relief in the manner described above.

It may be seen that, in all forms of the invention, the relative amounts of dye as measured from point to point over the finished image area differ from those obtained by simply dye imbibition processes.

In the accompanying drawings, e

Fig. 1 shows a set of three colour separation record silver negatives;

Fig. 2 shows a dyed set of three colour separation positive primary reliefs made from the negatives of Fig. 1;

Fig. 3 shows undyed, laterally reversed, green and red record positive secondary reliefs made from two of the"negatives "of 1 in'accordance with thepresentdnvention; w r l Figifii shows th'e fblu recbrdprimary relie sq iiegeedl together with the green record secondary relief; W Fig. 5 shows'the green record primary relief squeegeed together with the red record secondary relief; ,D

Fig. 6 shows thedyed 'set of 'colourseparation reliefs of Fig. 2, colour corrected for undesired blue and green absorption of the magenta and cyan dyes respectively; in accordance with the present invention.

' As an illustration of the invention, if it is de' sired to correct for the undesired blue absorption of the cyan dye, a secondary [relief is made through the samecoloured filter as that used for making the'cyan image and this secondary relief is squeegeed in register with the yellow dyed primary relief whereupon the yellowdye is shared between the two reliefs in accordance with the relative dye imbibition properties of the two reliefs at each point of the image, as shown in more detail hereinafter. In some cases the yellow dye can be introduced only by dyeing first the secondary relief, inwhich case the dye is shared although the intensities obtained at every point in the primary relief will not usually be thesame as would be obtained by dyeing only the primary relief, because the reliefs are not usually left in contact for the longtime which would be necessary to enable the dye distribution to reach equilibrium. r

An example illustrating the making of a three colour imbibitionpicturein which there is obtained, according to the invention, correction for the undesired blue. absorption of the magenta dye and also, undesired green absorption of the cyan dye is given below with reference to Figs. 1 to 6.

In Fig. 1, is shown a set of colour separation negatives, in which the blue record, negative silver image I l is contained in layer H), the green record negative silver image I3 is contained in layer 12, and the red record negative silver image [5 is contained inlayer [4. From each of these silver images is made, a gelatine primary image asshown in Fig. 2, .in which the blue record positive relief image I! is carried on a support IS, the green record positive relief I9 is carried on a support 18, and the red record positive relief image 2| is carried on asupport ZO. These reliefs can be checked for balance and density by dyeing them up in the respective subtractive coloured dyes and taking a print in the usual Way. When the primary set of reliefs is satisfactory, an extra (secondary) relief is made from each of the red and green record separation negatives, giving them exactly the same treatment as for those of the primary set, except that the negatives are turned over in the enlarger so that the secondary reliefs are laterally reversed with respect to the primary reliefs. These secondary reliefs are shown in Fig. 3, in which the green record positive secondary relief image 23 is carried on support 22, and red record positive secondary relief image 25 is carried on support 24. The three primary reliefs, l1, l9 and 2|, are now dyed up in bathslof cyan, magenta and yellow dyes respectively, the baths of magneta and yellow dyes. being at a higher concentration than usual in order to introduce a higher concentration than is usual into these two relief images. When this dyeing is complete, the yellow and magenta primary reliefs are rinsed in dilute acetic acid (for instance 1% depending upon the dye used) and the 'Inagen ta'primary relief is squeegeeddownin'register face to face with the laterally reversed secondary red record relief as r shown infFig. 4. It'can be seen that dye is taken out of the primary relief image areas whenever the secondaryrelief' image areas coincide therewith. The yellow primary relief is rinsed in dilute acetic acid andsqueegeed face to face with the laterally reversed green record relief, as shown in Fig. 5. The primary cyan relief is now rinsed in dilute acetic acid and squeegeed down in the normal way-onto a sheet of mordanted paper. 'Afterfive minutes, the magenta primary relief is stripped from the secondary relief and placed in a dish of dilute acetic acid. The cyan primary relief is removed from the mordanted paper and the magenta primary relief is squeegeeddown on the paper in the usual way. After, another five' minutes the yellow primary relief is stripped from the secondary relief and placed in a dish of dilute acetic acid. The magenta primary relief is then taken from the paper and replaced by h yellow primary'relief. After the yellow dye has thus been transferred to the paper, the desired-three colour print is obtained. The dye can be, washed out of the secondary reliefs so that they can be reused. Fig. 6 shows the three primary reliefs after colour correction and before printing, infwhich the shading of the blue and green record layers shows how dye has been removed from these layers whereverthere is dye in, the magenta and'cyan layers respectively. Thus, blue absorption: by the magenta dye and green absorption by the'cy'an dye 'is corrected.

Itis well known that in multicolour processes including those e'mploy'ing'colour correction it isvery desirable to so balance the overall'quantities of dye employed that at least neutral greys are reproduced '(i. e. fo r visual examination) with a reasonable accuracy. In the present process also, the concentration of dyes employed should be chosen with this in mind I 'It is apparentthat any of the dyes usually employed in dye imbibition processes may be used in my invention, although the optimum time of contact and the concentration employed may vary slightly from dye to dye as described above. The type of gelatine employed in the relief images or layers will also affect the optimum time of contact, soft or untanned gelatine reaching equilibrium more rapidly than hard or tanned gelatin in the manner well known to those skilledin the art.

One advantage of the process is that it'is not necessary to know in advance that colour-corary reliefs after a normal uncorrected dye transfer print has been made if it is considered that the result is unsatisfactory without correction and then a new corrected print can be made. Another advantage is that the process requires little or no more knowledge or skill on the part of the operator than the making ofuncorrected three-colour dye imbibition prints, and it is not necessary to do the somewhat laborious work of making correcting masks which require accurate densitometric control. The additional time taken in the transferring of the reliefs by this system is only about or 12 minutes.

The present invention can be applied to produce colour-correction of screen negatives for use in half-tone block making or photo-lithe plate making. The procedure is to make 'sepa-- ration negatives from which separation positive reliefs are made and in this case the correction is made in a somewhat similar manner to that described above for dye transfer print making, except that it is unnecessary to dye the positive reliefs up in different colours. For this purpose it would be sufficient to dye all the positive reliefs in a yellow dye since we are only concerned with the densities of the reliefs to blue light when screen negatives are made therefrom on blue-sensitive plates. Therefore, it is only necessary to make a set of three-colour positive primary reliefs and two secondary reliefs in exactly the same Way as described in the example above, except that all dye used is yellow dye. If desired, a colour print can be made from the same reliefs as a guide in subsequent operations, and this may often be a very big advantage to photomechanical workers when they are faced with the problem of reproducing transparencies. As the yellow dyed reliefs are to be used as positives, it is desirable to remove any silver therefrom. Alternatively, the dye from a set of reliefs can be transferred to a set of mordanted plain gelatine-coated plates.

The secondary reliefs used in the foregoing half-tone or photo-lithe rocess may also be used for making a black printer as follows.

Two secondary reliefs are made and used as y in the foregoing half-tone or photo-litho process, i. e. with the use of a yellow dye only, and also a third secondary relief is made as a laterally reversed blue record positive relief and the yellow-dyed red record positive primary relief is squeeged face to face in register therewith. There are then obtained three secondary reliefs each containing yellow dye extracted by all three secondary reliefs; where a primary colour was present in the original, dye will only be transferred to one of the secondary reliefs; and where a subtractive colour was present in the original, no dye will be tranferred to the secondary reliefs. The three dyed secondary reliefs can then be superposed, or dye from all three can be transferred to another (mordanted) layer in register. In either case, the composite image so obtained can be used as a printer by means of light so chosen in colour in relation to the dye, as to give a gamma suitable for a black printer for use with the three corrected yellow dyed positive primary reliefs.

For some photomechanical purposes it is desirable to have positives or negatives which have not a straight line tone reproduction charac- 6 teristic. This is particularly true in'the photolitho process where it is desirable to introduce curvature into the tone reproduction characteristics of the screen negatives. For instance, a uniform gelatine layer of the same thickness as the thickness part of the relief may be dyed in such a way that it takes up twice as much dye as is finally required in the thickest part of the relief. If the relief is now dyed by pressing it into contact with this uniform layer, the amount of dye taken up by the thickest part of the relief will be the same as would have been taken up in a bath of normal concentration and, of course, no dye is taken up where none would have been obtained anyway, while all the intermediate thicknesses will take up more dye than would have been the case in the dye bath. Choice of a suitable thickness of uniform gelatine dyeing matrix and concentration of dye makes it possible to obtain dye images of widely differing characteristics.

Colour correction combined with tone correction can also be obtained by means of the present invention. For instance, in order to obtain good whites in a photographic reproduction such as a print on paper it is of course necessary that the lighter tones must fall on the toe of the characteristic curve of the sensitive material employed. Where such a reproduction is made as a relief, tone correction for these lighter tones combined with colour correction for the remainder of the tones can be obtained by using as the secondary relief, one which has been made by giving less exposure to it than when colour correction is required without such tone correction; in this case the contrast of the secondary relief is preferably made greater than when colour correction without such tone corre'ction is required.

It will be apparent that since the proper working of the present invention depends upon the ability of the primary relief to share dye with another layer (secondary relief or a layer not bearing a relief image), it is important that these layers should not during the sharing process contain a mordant for the dye which is to be shared. In the application of the invention either to colour-correction or tone correction or both the amount of dye remaining in the primary relief must be sufficient to allow the dye image to be used for the production of the final three-colour picture.

What I claim is:

l. The method of making a colour corrected three colour photographic print by means of three dyed colour separation reliefs whose dye images are superimposed to give the desired print at least one of which dye images has both wanted and unwanted spectral absorption, wherein correction for unwanted absorption of a colour by dye having wanted and unwanted absorption in one of the colour separation reliefs is obtained by removing dye from the dyed relief which records the colour which is unwantedly absorbed by bringing it into contact and in register with an undyed relief image of the areas of the said unwanted absorption, and then combining the corrected relief thus obtained, with the remainder of said three-color separation reliefs to produce a color picture.

2. The method of making a colour corrected three colour photographic print by means of three colour separation reliefs dyed yellow, magenta and cyan respectively, whose dye images are superimposed to give the desired print,

wherein correction for .unwantedblue absorption by themagenta dye is obtained by removing dye from the yellow dyed relief by bringing itinto contact and in register with an undyed relief which is a green separation record, and thencombining the corrected. relief thus obtained, with the remainder of said three-color separation reliefs to produce a color picture.

3. The method of makinga colour corrected three colour photographicprint by means of three colour separation reliefs dyed yellow, magenta-and cyan respectively, whose dye images are-superimposed to give the desired print, wherein correction for unwanted green absorption by the cyan dye is obtained by removing dye from the magenta dyed relief by bringing it into contact and in register with an undyed relief which is a red separation record, and then combining the corrected relief thus obtained, with the remainder of said three-color separation reliefs to produce a color picture.

4. The method of making a colour corrected three colour photographic print by means of three colour separation reliefs dyed yellow, magenta .and cyan respectively, whose dye images are superimposed to give the desired print, wherein correction for undesired blue absorption by the cyan dye is obtained by removing dye from theyellow dyed relief by bringing it into contact and in registerwith an undyed relief which is a red separation record.

5. The method of makingv a colour corrected three colour photographic print by means of three colour separation reliefs dyed yellow, magenta and cyan respectively, whose dye images are superimposed to give the desired print, wherein correction for unwanted blue absorption by the magenta dye is obtained by removing dye from the yellow dyed relief by bringing it into contact and in register with an undyed relief which is a green separation record and wherein correction for unwanted green absorption by the cyan dye is obtained by removing dyefrom-themagenta dyed relief by bringing it into contact and in register with an undyed relief which is a red separation record, and then combining the corrected relief thus obtained, with the remainder of said three-color separation reliefs to produce a color picture.

6. In the method of making a three colour photographic print which comprises making three colour separation negatives through blue, green, and red filters respectively, making a primary gelatine positive relief from each of the said three negatives, dyeing the three reliefs so obtained yellow, magenta, and cyan respectively and printing from the three dyed reliefs in register, the steps of correcting for unwanted absorption of a colour by dye in one of the separation reliefs and of applying tone correction by removing dye from the dyed relief which records the colour which is unwantedly absorbed by bringing it into contact and in register with an undyed relief image of the areas of the said unwanted absorption except that it has been obtained by using less exposure than said dyed relief having saidv unwanted absorption, and then combining the corrected relief thus obtained, with the remainder of said three-color separation reliefs to produce a color picture.

DONALD C. GRESHAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,188,939 Ives June 27, 1916 1,976,152 Thornton Oct. 9, 1934 FOREIGN PATENTS Number Country Date 544,100 Great Britain Mar. 2'7, 1942 563,834 Great Britain Aug. 31, 1944 

1. THE METHOD OF MAKING A COLOR CORRECTED THREE COLOUR PHOTOGRAPHIC PRINT BY MEANS OF THREE DYED COLOUR SEPARATION RELIEFS WHOSE DYE IMAGES ARE SUPERIMPOSED TO GIVE THE DESIRED PRINT AT LEAST ONE OF WHICH DYE IMAGES HAS BOTH WANTED AND UNWANTED SPECTRAL ABSORPTION, WHEREIN CORRECTION FOR UNWANTED ABSORPTION OF A COLOUR BY DYE HAVING WANTED AND UNWANTED ABSORPTION IN ONE OF THE COLOUR SEPARATION RELIEFS IS OBTAINED BY REMOVING DYE FROM THE DYED RELIEF WHICH RECORDS THE COLOUR WHICH IS UNWANTEDLY ABSORBED BY BRINGING IT INTO CONTACT AND IN REGISTER WITH AN UNDYED RELIEF IMAGE OF THE AREAS OF THE SAID UNWANTED ABSORPTIOM, AND THEN CONTINING THE CORRECTED RELIEF THUS OBTAINED, WITH THE REMAINDER OF SAID THREE-COLOR SEPARATION RELIEFS TO PRODUCE A COLOR PICTURE. 